Children born with severe heart abnormalities often require surgery in the newborn period. Children born with only one ventricle in their heart require a staged palliation, the Fontan series, to convert their heart to a normal circulation in which the oxygenated ("red") and unoxygenated blood ("blue") are separated. Intra-atrial reentrant tachycardia, an abnormal fast heart rhythm in the top chambers of the heart, is a well recognized sequelae of the Fontan operation. The incidence of both early and late intra-atrial reentrant tachycardia is 10-35%. Data from animal models as well as human studies suggest that suture lines used in the Fontan operation in combination with natural anatomical right atrial boundaries (vena cava orifices, coronary sinus orifice, tricuspid valve, and possibly the crista terminalis) can serve as barriers creating a pathway which, along with changes in intra-atrial conduction, provide the substrate for an intra-atrial reentrant tachycardia. The objective of this study is to investigate if a strategically placed linear incision, incorporated at the completion of the Fontan, will prevent the postoperative intra-atrial arrhythmia. The study is a randomized prospective design in which candidate patients will receive either the conventional Fontan operation (control group), or a fenestrated Fontan repair with a cryosurgery lesion or surgical incision (test group). The primary endpoint will be based upon the failure to induce the intra-atrial reentrant tachycardia in the test group compared to the control group both during the immediate post operative period (prior to hospital discharge). The patient groups will also be followed for a five year period to determine the effect of the surgical incisional lesion on the prevention of late clinical reentrant intra-atrial tachycardia.